Ontogenetic Changes of Proteins of Endoplasmic Reticulum

Abstract

The proteins of the smooth and rough endoplasmic reticulum from fetal, immature, and adult male rats were compared after incorporation of two radioactively labeled precursors, "C-labeled amino acids and S-aminolevulinic acid 3 H by means of gel electrophoresis. The labeling patterns indicated that protein components present in two major electrophoretic bands underwent significant synthesis in fetal tissue while three actively incorporating protein bands were noted in adult tissue . Although the uptake of the amino acids-'4 C decreased for the smooth and rough elements of the endoplasmic reticulum as a whole during liver development, the qualitative patterns were not significantly different in adult and fetal livers . The over-all incorporation (disintegrations per minute per milligram protein) of the heme precursor into the smooth and rough elements also did not change with development . However, a change was noted in the distributional electrophoretic patterns with development . The estimation of molecular weight (by disc electrophoresis) and the incorporation of the heme precursor suggested the similarity of the two major protein bands to cytochrome P-450 and cytochrome b5 , components of the endoplasmic reticulum, thought to be involved in the mixed-function oxidase system . The evidence indicated that in fetal liver, at a time when the oxidase capability was low, the amino acid incorporation into these two protein groups was the same as in the adult . The incorporation of the heme moiety, however, was different, decreasing in the cytochrome b 5 region and increasing in the cytochrome P-450 region during development . These results correlate with the increase in oxidase activity associated with liver development .

The differentiation of rat liver endoplasmic reticulum membranes: Apo–cytochrome P450 as a membrane protein

“…The results point to the conclusion that during differentiation of the ER membranes, at least one protein, cyt P450, is present in an inactive form, without its heme moiety, and that differentiation consists, in part, of the attachment of heme to the apo-protein concomitant with an increase in the proportion of this protein in the membranes. A similar conclusion has been reached for this cytochrome based on preliminary evidence (53).…”

“…This result, which confirms an earlier one (45), is not too surprising since the hemes of cyt P4so and cyt bs are noncovalently bound to the proteins, can be removed by 7 M urea (52), and have been shown recently to be also removed by SDS (45). A contrary finding has been found, that is, a retention on SDS gels of label from ,'-ALA injection (53); but this may possibly be due to a dissociation and reassociation of heme to proteins on the gel under the conditions of the experiment, as will be explained below. Schatz et al (54) have found that by treating mitochondria1 fractions with alkaline h'ig.…”

“…A major staining band from ER membranes with a similar molecular weight, from 52,000-55,000, has already been observed by Hinman and Phillips ( 3 2 ) , Schnaitman (37), Neville and Glossmann (39), and Black and Bresnick (53), with the latter also tentatively identifying it as the apo-protein of cyt P450. Figure 6 shows the scans of gels after electrophoresis of proteins obtained from the liver ER membranes of rats of various ages.…”

Modulation of Monooxygenase Activities by Hematin and 7 ,8-Benzoflavone in Fetal Tissues of Rats, Rabbits, and Humans1

“…1 Added BF was dissolved in 10 µl ethanol. 2 These assays were performed on fresh tissue preparations. 3 These assays employed tissues which had been previously frozen ( -80 °C; 1 weck).…”

Functional maturation of cytochromes P450 3A4 and 2D6 relies on GAPDH- and Hsp90-Dependent heme allocation

“…In particular, it is still unclear how heme generated in the mitochondria is delivered and inserted into CYP proteins. Early studies suggested that CYP heme acquisition might occur in concert with their protein expression ( 13 ), but other studies indicated that CYP proteins may build up in their heme-free forms during their maturation ( 14 , 15 ), particularly in tissues other than the liver including the brain, lung, and kidney ( 16 , 17 ). Given the propensity of CYP’s to attach to the ER, it has also been suggested that heme delivery to such proteins might occur through mitochondrial-ER membrane contact ( 18 ).…”